The genus Gerbillus (Mammalia: Rodentia) is characterized by an important morphological homogeneity associated with an extensive karyotypic diversity. Here we describe a new species of Gerbillus from the Inner Delta of the Niger River in Mali, on the basis of morphological and chromosomal data. This new species seems to be morphologically very similar to G. campestris, another bare-footed species known from northern Africa. Nevertheless, it can be distinguished from the latter species by a different molar pattern and a specific karyotype. The three specimens on which this description is based were caught in a rocky outcrop, and behavioural observations in captivity suggest an adaptation to life in rocky habitats. This finding is unusual as rodents of the genus Gerbillus are generally sand-dwellers. Moreover, this new species enriches the gerbil community of this Sahelian region, in which at least nine species of the genus can be found. Finally, this description highlights the importance of chromosomal studies for the characterization of biological diversity in tropical rodents, where morphological sibling species are numerous.